PROJECT 3: Malignant gliomas are uniformly fatal tumors and there is an urgent need for improving our biological understanding of these lesions in order to rationally develop treatments. Molecular imaging can be adopted for interrogating the complex oncogenic pathways which impact their aggressive phenotype. Furthermore, targeted disruption of one or several signaling processes at once may provide an avenue for improving the overall survival of patients. However, the interconnecting pathways can provide tumors with redundancies in the signaling cascades allowing for it to adapt and thereby evade treatment. Moreover, recent studies have shown that gliomas also contain a therapeutically resistant subpopulation of cancer stem cells which can provide for repopulation of the mass following conventional therapeutic interventions. Therefore, in this Project, we seek a paradigm shift in approaching the development of improved therapeutic strategies for neurooncology patients by development and incorporation of novel molecular imaging tools to address three key aspects believed to frustrate current treatment of gliomas: (1) Unknown effects of inhibiting signaling molecules on other signaling pathways and how the glioma cell can evade treatment using redundancies (escape routes) within the interconnected signaling pathways (2) How these signaling pathways differ in the glioma stem cell population and;(3) How we can use this information to eliminate the glioma stem cell population along with the bulk mass of cells within the tumor site. Optical molecular imaging reporters for key molecular events including Met kinase activity, Akt kinase activity, EGFR activity and Caspase-3 will be expressed in human glioma cells and used as readouts for evaluating the response of treatment interventions on the oncogenic signaling activities in the glioma stem and non-stem cell populations both in vitro and in vivo. We will engineer a human glioma cell line such that CD133 expression will correlate with bioluminescence activity. This will enable us to quantify the growth and survival of the tumor stem cell population. The ability to monitor tumor burden using MRI as well as the cancer stem cell population using this engineered reporter line will result in the identification and validation of novel treatments/combinations wherein cancer stem cell dependent repopulation is delayed and thereby improving the clinical outcome of brain tumor patients. Public Health: The studies proposed here will provide the foundation of incorporating molecular imaging reporters and applications into the drug development and evaluation process for improving our understanding treatment resistance which should lead to a more rationale approach for selection of treatments. Overall, the success of this Project will lead to improved survival of patients with gliomas.